Ya know, I think I read somewhere (was it on TPU?) that the throttle is there to also protect the mobo, as well as the card. However, I don't quite understand why motherboard damage could happen: the PCI-E slot is rated for 75W, so the card will simply pull a max of 75W from there, in order to stay PCI-E compliant and the rest through its power connectors, therefore the risk to the mobo shouldn't be there.

That is what can happen if you overload the PCI-e slots. Now that was an extreme case of course, but once you start pulling more than 75w through the PCI-E connector things can get hairy pretty quickly.

That is what can happen if you overload the PCI-e slots. Now that was an extreme case of course, but once you start pulling more than 75w through the PCI-E connector things can get hairy pretty quickly.

But my point is that wouldn't the card limit its power draw to stay within that limit and pull the rest from it's power connectors? That would prevent any damage to the mobo and stay PCI-E standards compliant. I don't know if it would, which is why I'm throwing the question out to the community.

But my point is that wouldn't the card limit its power draw to stay within that limit and pull the rest from it's power connectors? That would prevent any damage to the mobo and stay PCI-E standards compliant. I don't know if it would, which is why I'm throwing the question out to the community.

That is pretty much the idea behind this limit. The PCI-E slot provides 75w, a 6-pin PCI-E power connector provies 75w, and an 8-pin PCI-E power connector provides 150w. That is 300w. So once you go over that, it doesn't matter if the power is coming from the PCI-E power connectors or the motherboard's PCI-E slot, you are overloading something somewhere, and you aren't PCI-E standards compliant.

Sure something would go pop, but it still doesn't answer the question if the card would pull more than 75W from the mobo under such a condition. Properly designed, it should limit the current. I just don't know if it does or not and I don't think anyone else does either.

Sure something would go pop, but it still doesn't answer the question if the card would pull more than 75W from the mobo under such a condition. Properly designed, it should limit the current. I just don't know if it does or not and I don't think anyone else does either.

W1z might know if he has power consumption numbers from just the PCI-E slot.

However, if you assume pretty even load across all the connectors, 1/4 from the PCI-E slot, 1/4 from the PCI-E 6-pin, and 1/2 from the PCI-E 8-Pin, once the power consumption goes over 300w, the extra will be divided between all the connectors supplying power. I don't believe the power curcuits on video cards are smart enough to know that once the power consumption goes over a certain level to load certain connectors more than others.

Ya know, I think I read somewhere (was it on TPU?) that the throttle is there to also protect the mobo, as well as the card. However, I don't quite understand why motherboard damage could happen: the PCI-E slot is rated for 75W, so the card will simply pull a max of 75W from there, in order to stay PCI-E compliant and the rest through its power connectors, therefore the risk to the mobo shouldn't be there.

People privy to inside information, and who are smarter than you and I, decided it was necessary.

I suspect the tech specs published to manufacturers didn't account for the unusual power consumption under furmark etc. This wouldn't have been an accident, but rather a procedure to keep costs down re power circuits and cooling.

I don't believe the logic exists for that either, I believe some cards pull the memory and other power through the PCIe slot and the core power through he connectors. I hope that is how they have the 580 setup.

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@ bakalu: Any chance you could rename the EXE Furmark to whatever you like and run it again with your 580? If @ anytime you see the temp rising too much, please interrupt the program but do post a screenie after.

Ya know, I think I read somewhere (was it on TPU?) that the throttle is there to also protect the mobo, as well as the card. However, I don't quite understand why motherboard damage could happen: the PCI-E slot is rated for 75W, so the card will simply pull a max of 75W from there, in order to stay PCI-E compliant and the rest through its power connectors, therefore the risk to the mobo shouldn't be there.

That is pretty much the idea behind this limit. The PCI-E slot provides 75w, a 6-pin PCI-E power connector provies 75w, and an 8-pin PCI-E power connector provides 150w. That is 300w. So once you go over that, it doesn't matter if the power is coming from the PCI-E power connectors or the motherboard's PCI-E slot, you are overloading something somewhere, and you aren't PCI-E standards compliant.

I'm not 100% sure, but I don't think so. A card expecting 150W from the slot would not run on a 1.0 slot, but the compatibility is 100%. The additional W come from the external connectors.
75W+2x75W from 2x6Pins makes 225. 8-pins are used if power drain is larger then 225W.
A PCI-E with 150W from slot could get to 350+ with the extra 8-pins, which is not the case.

I'm not 100% sure, but I don't think so. A card expecting 150W from the slot would not run on a 1.0 slot, but the compatibility is 100%. The additional W come from the external connectors.
75W+2x75W from 2x6Pins makes 225. 8-pins are used if power drain is larger then 225W.
A PCI-E with 150W from slot could get to 350+ with the extra 8-pins, which is not the case.

drawing more than 75W from the slot wont magically turn the slot off, or anything else like that... if the card has no internal mechanism to deal with the power draw, the wiring feeding the slot will just start to overheat, and bad things can happen.